Was Tyrannosaurus rex a predator or a scavenger?

Cretaceous Hyenas: Tyrannosaur Opportunists

A brown water snake, armless, eats a sizable catfish.
A brown water snake, armless, eats a sizable catfish.

One possible discovery could offer proof that Tyrannosaurus rex was a scavenger -- evidence of healed-over tyrannosaur bites in other fossils. Most fossilized dinosaurs died from events unrelated to being eaten, so it should be easy to tell whether they survived past attacks from predators. Unfortunately, there are few fossils that show clear evidence of past T. rex bites.

John W. Happ of Shenandoah University suggests a Triceratops whose skull was discovered in 1997 lived for years after being bitten by a T. rex [source: Perkins]. An Edmontosaurus fossil shows evidence of vertebral spines that re-grew after a bite that may have been inflicted by a tyrannosaur [source: Carpenter]. But there are few such examples, and the cause of the bone damage is difficult to prove conclusively. There's also the question of whether any animal would survive long enough for its T. rex bite to heal.

Some of the same evidence used to suggest that T. rex may have been a predator can be interpreted differently. For example, T. rex had tiny arms, especially compared to the prehistoric raptors. But some researchers point out that armlike forelimbs aren't a prerequisite for being a predator -- snakes, for instance, manage without them. One study also defies the idea that these limbs were useless. Kenneth Carpenter of the Denver Museum of Natural History suggests that based on the size, shape and position of the arm bones and shoulder blades, these apparently puny limbs were powerful.

Then there's the matter of the abundance of broken dinosaur teeth some interpret as evidence of eating abandoned bones. If T. rex was a predator, it might have used one of many methods to attack prey, and each could have resulted in broken teeth. Tyrannosaurs might have:

  • Ripped through the neck or throat, causing teeth to meet vertebrae and the skull
  • Charged at prey with its mouth wide open to inflict a devastating wound, breaking teeth on whatever bones it hit
  • Attacked with a bite to the abdomen, hitting ribs in the process

Plus, an animal as large as T. rex may have needed bones for nourishment regardless of whether it killed an animal or found a corpse.

This counterargument even gets down to the defense mechanisms of T. rex's potential prey. Was the neck frill on a Triceratops for protection or sexual display? And did it use its horn for defense against predators or combat with intruders on its territory? Since we have no way to observe the behavior of these animals, we don't really know. The most logical answer may be that Tyrannosaurus rex, like many large predators, was an opportunist, catching fresh meat when possible and eating carrion when necessary.

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